Recently, as electronic equipment with higher performance is smaller and thinner, it is required to mount electronic components in a higher density on a printed circuit board and to more highly enhance the function of a circuit board on which the electronic components are mounted. In this situation, a module with a built-in component (or a circuit board with a built-in component), that is, a circuit board in which an electronic component is embedded has been developed (see Japanese Patent Kokai (Laid-Open)) Publication No. 11 (1999)-220262(A).
An area surface of the module with a built-in component is reduced since electronic components such as an active component (such as a semiconductor device) and a passive component (such as a capacitor), which are generally mounted on a surface of a printed board (or printed circuit board), are embedded in the substrate. An improvement in high frequency property can be achieved in the module with a built-in component by an appropriate wiring between electronic components since the freedom of positioning of the electronic components is higher compared with the surface component mounting.
In the field of a ceramic board, a LTCC (low temperature cofired ceramics) board into which an electronic component is incorporated has already practically been employed. However, there are many limitations for the LTCC board. For example, it is difficult to apply this board to a large-sized board because this board is heavy and susceptible to fracture. Further, since this board is produced through a high temperature cofire, a semiconductor device such as an LSI cannot be embedded in the board. Recently, another module with a built-in component wherein a component is disposed within a printed resin board attracts attention. The resin circuit board has no limitation on size unlike with the LTCC board, and has an advantage that LSI can be disposed within the board.
Next, the module with a built-in component (or a module with a built-in circuit component) disclosed in Japanese Patent Kokai (Laid-Open)) Publication No. 11 (1999)-220262(A) is described with reference to FIG. 1. The module with a built-in circuit component 400 consists of a substrate 401 formed by stacking insulating substrates 401a, 401b and 401, wiring patterns (or wiring layers) 402a, 402b, 402c and 402d formed on and inside the substrate 401, and circuit components 403a and 403b which are disposed within the substrate 401 and connected to the wiring patterns. The wiring patterns 402a, 402b, 402c and 402d are electrically connected through inner vias 404. The insulating substrates 401a, 401b and 401c are formed of, for example, a mixture containing an inorganic filler and a thermosetting resin.
The electrical connection of the wiring patterns 402a, 402b, 402c and 402d to each other are made by the inner vias 404 in the module with a built-in circuit component 400 as shown in Japanese Patent Kokai (Laid-Open) Publication No. 11 (1999)-220262(A). The inner via connection method is preferably employed since it enables the desired wiring patterns to be connected and the circuit components are well mounted. In the conventional component circuit boards including the module with a built-in circuit component 400 as shown in FIG. 11, the electrical conduction between an upper surface and a lower surface is ensured by the inner via or a through hole.
Based on the technical common knowledge in the field of printed wiring board and built-up wiring board, the inner via or the through hole has to be formed for producing the module with a built-in component. The via formation requires a step of forming a through hole and a step of filling the hole with a conductive paste or a step of plating the hole, which make the via forming process complicated. However, these steps are essential and it difficult to develop a more efficient production method without these steps. Further, the connection by the via requires a connection element such as a land, which increases the size of the module by the area occupied by the connection element. Further, the freedom of condition of compatibility of the electronic component incorporation and the via formation (for example, a viscosity of a resin mixture for insulating substrate) is low, whereby wire bonding may be difficult.